The overall objective is to investigate masses, volumes, flow rates, blood-tissue transport mechanisms and metabolism in mammalian tissues, organs and the whole body by means of multiple tracer and osmotic indicator dilution experiments. The proposed work consists of determining (a) the tracer permeability and the reflection coefficient of the lung endothelial and epithelial barriers to water, (c) masses, volumes of distribution, and imput and output rates of various body substances and carrier fluids in the whole body from tracer kinetic measurements in the plasma, (d) to set up mathematical models of distribution of tracer substances and osmotically active substances passing through tissues, organs and the whole body which relate such measurable results of indicator dilution experiments as concentrations or specific activities vs time to independently measurable physiological parameters such as blood flow, volume of distribution, permeability, reflection and filtration coefficients, diffusion coefficients, metabolic rates, (e) to determine tracer permeability of cell membranes by measurement of bulk diffusion coefficients through "tissues" of packed cells. BIBLIOGRAPHIC REFERENCES: Perl, W., P. Chowdhury and F.P. Chinard. Reflection coefficients of dog lung endothelium to small hydrophilic solutes. Am. J. Physiol. 228: 797-809, 1975. Perl, W. Red cell permeability effect on the mean transit time of an indicator transported through an organ by red cells and plasma. Circulation Res. 36: 352-357, 1975.